Vertical tailplanes or vertical stabilizers of aircraft serve to control and stabilize the aircraft about the vertical or yaw axis. The corresponding action of the vertical stabilizer can be adapted to the respective situation by changing the angular position of the rudder.
The aerodynamic effect of a vertical stabilizer is based to a significant extent on the flow profile which is established in operation of the aircraft at the surfaces of the fin and the rudder. However, with increasing angle of attack flow separation or stall may occur, in which condition the flow no longer follows the respective surface, but separates and moves away from the surface, and the rudder loses at least part of its effect. The separation of the flow occurs primarily if the boundary layer above the surface does not include sufficient energy for maintaining the flow along the surface contour.
Large angles of attack at the vertical stabilizer occur primarily if the aircraft velocity is relatively low and the rudder is strongly deflected. A strong deflection of the rudder is required in particular if thrust is decreasing on one side due to malfunction or failure of engines and steering in the opposite direction must be effected by the rudder in order to maintain the course of the aircraft. Angles of deflection of the rudder, which occur in the case of such an error condition and which reach or exceed, e.g., 25° or 30°, are not required during normal operation. Therefore, there is a need for particular measures for preventing flow separation and stall in particular in this error condition or in other flight or operation situations in which such a strong deflection of the rudder is necessary.
Vortex generators, which are also referred to as swirl vanes or turbulence generators, are projections located on surfaces of aircraft components over which flow occurs, which projections are configured and arranged to selectively generate vortices or turbulence in the boundary layer region of the flow and, in this manner, to supply the flow with energy and maintain the flow along the surface. Thereby a flow separation can be prevented or delayed, and it is possible to realize larger angles of attack without flow separation and stall. However, vortex generators always also cause an increase of drag and flow resistance so that they are associated with disadvantages outside such flight or operation situations. For this reason vortex generators are known which are selectively extendable and retractable or selectively unfoldable and foldable and which are preferably only extended or unfolded if required and are otherwise retracted or folded in in order not to increase the flow resistance.